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CVE-2026-18209— Keycloak-services: keycloak-services: oidc redirect_uri fragment bypass in http parameter pollution check

Quick assessment

Affected
Red Hat Red Hat build of Keycloak 26.6
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Keycloak是Keycloak组织开源的一种身份和访问管理解决方案。 Keycloak存在输入验证错误漏洞，该漏洞源于keycloak-services组件中用于防止HTTP参数污染的安全检查仅检查重定向URL的查询部分而忽略片段部分，可能导致攻击者注入重复安全参数，若客户端应用配置不正确，则可能信任注入数据，导致会话固定或账户混淆。

CVSS 3.4 · Low EPSS 0.41% · P35

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application

Affected Version Matrix 9

VendorProduct Version RangeStatus
Red Hat Red Hat build of Keycloak 26.6 26.6.7-3< * unaffected
26.6-20< * unaffected
26.6-20< * unaffected
Red Hat Red Hat build of Keycloak 26.6.7 any unaffected
any unaffected
any unaffected
Red Hat Red Hat Data Grid 8 any unaffected
Red Hat Red Hat JBoss Enterprise Application Platform Expansion Pack any unaffected
Red Hat Red Hat Single Sign-On 7 any unaffected
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I. Basic Information for CVE-2026-18209

Vulnerability Information
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Vulnerability Title
Keycloak-services: keycloak-services: oidc redirect_uri fragment bypass in http parameter pollution check
Source: CVE Program / CVE List V5
Vulnerability Description
A flaw was found in the keycloak-services component of Keycloak, which handles OpenID Connect (OIDC) authentication flows. The issue occurs because the security check designed to prevent HTTP parameter pollution only inspects the query portion of a redirect URL and ignores the fragment portion. When a client is configured with a wildcard redirect URI, an attacker can use this to inject duplicate security parameters into the login response. If a client application is not configured correctly, it might trust the attacker's injected data instead of the real security information from Keycloak, leading to session fixation or account confusion.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:N/I:L/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
CWE-1288
Source: CVE Program / CVE List V5
Vulnerability Title
Keycloak 输入验证错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Keycloak是Keycloak组织开源的一种身份和访问管理解决方案。 Keycloak存在输入验证错误漏洞，该漏洞源于keycloak-services组件中用于防止HTTP参数污染的安全检查仅检查重定向URL的查询部分而忽略片段部分，可能导致攻击者注入重复安全参数，若客户端应用配置不正确，则可能信任注入数据，导致会话固定或账户混淆。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
Red Hat Red Hat build of Keycloak 26.6 26.6.7-3 ~ * cpe:/a:redhat:build_keycloak:26.6::el9
Red Hat Red Hat build of Keycloak 26.6 26.6-20 ~ * cpe:/a:redhat:build_keycloak:26.6::el9
Red Hat Red Hat build of Keycloak 26.6 26.6-20 ~ * cpe:/a:redhat:build_keycloak:26.6::el9
Red Hat Red Hat build of Keycloak 26.6.7 - cpe:/a:redhat:build_keycloak:26.6::el9
Red Hat Red Hat build of Keycloak 26.6.7 - cpe:/a:redhat:build_keycloak:26.6::el9
Red Hat Red Hat build of Keycloak 26.6.7 - cpe:/a:redhat:build_keycloak:26.6::el9
Red Hat Red Hat Data Grid 8 - cpe:/a:redhat:jboss_data_grid:8
Red Hat Red Hat JBoss Enterprise Application Platform Expansion Pack - cpe:/a:redhat:jbosseapxp
Red Hat Red Hat Single Sign-On 7 - cpe:/a:redhat:red_hat_single_sign_on:7

II. Public POCs for CVE-2026-18209

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III. Intelligence Information for CVE-2026-18209

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Vendor Advisories for CVE-2026-18209 (4)

Same Patch Batch · Red Hat · 2026-07-31 · 14 CVEs total

CVE-2026-10079 8.5 HIGH Stackrox: stackrox: deploy-time policy enforcement and visibility bypass via label injecti
CVE-2026-18141 8.2 HIGH Aap-gateway: aap-gateway: authentication bypass in event-driven ansible via forged http he
CVE-2026-15722 7.5 HIGH 389-ds-base: 389-ds-base: pre-authentication stack buffer overflow in get_ruvelement_from_
CVE-2026-11770 7.5 HIGH 389-ds-base: 389-ds-base: pre-auth ldap filter injection in cleanallruv status check
CVE-2026-18215 6.8 MEDIUM Keycloak-services: keycloak-services: microsoft external access-token exchange bypasses co
CVE-2026-18214 6.8 MEDIUM Keycloak-services: keycloak-services: google external access-token exchange bypasses hoste
CVE-2026-18208 6.5 MEDIUM Keycloak-services: keycloak-services: inactive out-of-audience token introspection leaks s
CVE-2026-18203 6.5 MEDIUM Keycloak-services: keycloak-services: group policy extendchildren matches sibling group pa
CVE-2026-16105 4.9 MEDIUM Keycloak-services: keycloak-services: missing per-role authorization on rolecontainerresou
CVE-2026-18218 4.2 MEDIUM Keycloak-services: keycloak-services: client not-before revocation ignored when realm not-
CVE-2026-18211 4.2 MEDIUM Keycloak-services: keycloak-services: secure-client-uris policy bypass via localhost-prefi
CVE-2026-18206 3.7 LOW Keycloak-services: keycloak-services: client policy source-host wildcard domain matching b
CVE-2026-18217 3.4 LOW Keycloak-services: keycloak-services: saml http-redirect binding response preserves query

IV. Related Vulnerabilities

Same product: Red Hat build of Keycloak 26.6
Same vendor: Red Hat
Same weakness: CWE-1288